Symptoms
- Air filter visibly wet or dark with oil
- Strong fuel smell coming from the filter housing
- Engine runs rough or hard to start after refueling
- Oily residue inside the air filter cover
Likely causes
- CommonStoring the trimmer on its side or upside downFuel and oil can seep into the air filter housing when stored in the wrong position.
- CommonFuel mix with too much oilAn overly rich oil ratio increases the chance of oil residue reaching the filter.
- PossibleCarburetor flooding from a stuck float or over-primingExcess fuel can back up into the air intake path.
- PossibleWorn crankcase sealsOn 2-stroke engines, failing crankshaft seals can push oil into the intake.
- Less commonOverfilled or leaking fuel tankA tank filled past capacity can weep fuel into nearby components.
What to do
- Remove and clean or replace the soaked air filter; a foam filter can often be washed in mild soapy water and dried fully before reuse.
- Check that your fuel is mixed at the correct ratio specified in the manual, not richer than recommended.
- Always store the trimmer upright, following the manufacturer's recommended storage position.
- Inspect the primer bulb and carburetor for signs of over-fueling or a stuck float if flooding seems to be the cause.
- Check the fuel tank fill level and cap seal for leaks.
- If oil continues to appear in the filter housing repeatedly, have the crankcase seals inspected, since this points to an internal engine issue.
- Reinstall a clean, dry filter before running the trimmer again.
Tools and parts
- Mild dish soap
- Clean towel
- Replacement air filter
Air filterSearch: “trimmer air filter replacement”
Crankcase seal kitSearch: “small engine crankshaft seal kit”
When to call a pro
If oil keeps soaking the filter after correcting storage and fuel mix, a small-engine shop should check the crankcase seals.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.